1. Field of the Invention
This invention relates to multi-layer modules that provide physical support and electrical connection to a very large-scale integrated circuit chip or chips mounted thereon by means of a dense array of via connectors, and more particularly, to an improved module that includes a heater to control the module surface temperature.
2. Description of the Prior Art
As will be appreciated by those skilled in the art, multi-layer modules are used to mechanically support and electrically connect integrated circuit chips mounted on the module. Both single chip modules and multiple-chip modules are known in the art. Such modules are made typically of a number of individual ceramic or glass ceramic sheets that have been fused together to form the module. Solder balls connect one or more integrated circuit chip electrically and mechanically to the top surface of the module.
In manufacturing the module, individual layers or sheets are formed with desired wiring patterns and/or vias. Ceramic or glass ceramic sheets which are commonly used have desired wiring patterns formed on their surface and via openings formed by a punch. The sheets are stacked and sintered to fuse them together to form a solid module block. In a typical multi-layer module, the spacing among the top layer vias connecting the solder bumps to lower layers in the module is extremely close.
While generally quite satisfactory, such multi-layer ceramic modules have several temperature related shortcomings.
If an integrated circuit chip must be removed from a module as a result of failure during burn-in, or for any reason, solder bumps are often damaged in the process of removing the chip, which makes replacement of the chip difficult and costly or impossible.
In addition, the coefficients of thermal expansion of the integrated circuit chip and the ceramic module itself are usually different. This limits the maximum chip size (distance from a neutral point) and limits the operational life of the connectors due to the mechanical strain caused by differential thermal expansion as the temperature of the module changes in power on, power off machine cycles.
In a multi-chip module, all chips on the module should be within a rather narrow temperature range during operation. In prior art modules, this need to keep all chips within a relatively narrow temperature range limited module design flexibility, since high-power chips could not be used with low-power chips where local heating in the region of the high-power chip would create a temperature differential outside an acceptable range between high-power and low-power chips.
There have been proposals in the prior art addressing some of these issues in the context of relatively simple chips mounted on printed circuit boards.
U.S. Pat. No. 5,010,233 to Henschen et al. discloses a heater secured to or embedded in a circuit board. The heater is selectively energizable to melt solder in a connection or disconnection operation. The heater is spaced from circuit board contact pads by circuit board structure material that transmits the generated thermal energy to the contact pads to melt solder or other fusible material.
U.S. Pat. No. 4,374,316 to Inamori et al. discloses a semiconductor integrated circuit support on which a heating element is provided. The support comprises a package, a printed circuit board, a mother board, or the like, for supporting a semiconductor integrated circuit, which includes devices such as transistors. The heating element is capable of heating the whole, or a required part only thereof, so that the semiconductor integrated circuit is preheated to a temperature required for its normal operation with precision and stability.
U.S. Pat. No. 4,769,525 to Leatham discloses a circuit package, or other device, mounted on a printed circuit board, or other substrate, with an electrically conductive sinuous resistor wire structure therebetween in a space filled with adhesive. When the adhesive is set the package is held in place. When removal is desired, current is passed through the sinuous wire structure to soften the adhesive to permit removal of the package without damage to the package or the board.
U.S. Pat. No. 4,506,139 to Daughton discloses a hybrid or integrated circuit chip with a heating means integral therewith. The heating means is made accessible for application of an external electrical energy source so as to permit removal of the circuit chip after previously being soldered to a support structure or permit soldering of a circuit chip to the support structure.
U.S. Pat. No. 4,582,975 to Daughton discloses a method for removing a hybrid or integrated circuit chip soldered to a support structure. An electrical energy source is applied to the hybrid circuit chip for raising the temperature of the circuit chip sufficiently so as to melt the solderable material which interconnects the chip to the support structure. When the solderable material is melted, the circuit chip may then be removed from the support structure.
U.S. Pat. No. 3,584,189 to Marcous discloses a self-regulating heater for integrated circuits and the like which are removably carried in a connector assembly. The heater includes a heating element composed of material having a positive temperature coefficient of resistance. The heating element is pressed against a heater plate. A rim of the heater plate is supported upon the margin of an opening or window in the housing so that an integrated circuit unit or the like mounted on the housing, is placed in heat-exchange relationship with the heater plate, whereby the temperature of the integrated circuit unit or the like is stabilized. Interchange may readily be made between various heater elements to provide desired changes in the regulated temperature.
U.S. Pat. No. 3,440,407 to Goltsos et al. discloses a circuit board having a grid of resistance heating elements embedded in an insulating substrate. The heating of the board can be localized by severing the grid at strategic points. A thermostat is orientated to control the temperature at selected portions of the board.
U.S. Pat. No. 4,481,403 to Del Monte discloses a controlled heater apparatus for selectively heating a solid state circuit chip and the substrate upon which it is mounted by a solder bump, so as to cause substantially equal expansion and contraction in the chip and substrate to relieve stress on the connecting solder bump.
It will be appreciated that these prior art proposals address some issues, such as chip removal for example, addressed by this invention. However, the context of these prior art proposals is different than that of a multi-layer ceramic module with its dense top surface via pattern.